1. Field of the Invention
The present invention relates to the art of illuminating television studios and video-tape production facilities or the like, and more particularly concerns an improved method of lighting studios, and an improved fixture which may be used to carry out the new method.
2. Description of the Prior Art
As television grew and became an industry there was an electronic revolution. There was first a standardization in television systems, then an energetic refinement in the equipment that processed visual information.
While there were great advances made in the camera and image processing systems, there was little if any concern given to what is perhaps the most crucial element of visual media--light.
Lighting fixtures for early television stations were a combination of theatrical and motion picture lighting equipment. These lighting fixtures were created to send as much light from a single source as possible. Consumption of power was rated in kilowatts and the more a fixture required the better. This was a proper and necessary approach as cameras were in a crude stage of development and the higher the light quantity the better the resultant picture would be. The resultant picture by today's standards was monocromatic (black and white), high in contrast and low in detail.
Today the technology that supports camera imagery and television signal processing is highly developed. Cameras have been constructed that measure the very subtle qualities of light. Quantity is not the most important factor in lighting. Many cameras have threshold levels of low footcandle values.
Today the technology that supports television studio lighting is the same technology which launched television. Minor refinements have not changed the basic premise that the most light generated is best.
The intense amount of light coming from a single source fixture has presented some problems. People appearing on camera often have shadows crisscrossing their features. The heat and intensity of conventional lighting often causes oncamera people to perspire. The heat generated by conventional lighting demands an immense energy requirement to cool the rooms in which they operate. Many of the special effects used in television broadcast and video production require that the light levels and quality of light within a scene be evenly distributed. Should the light be uneven, visual distortion or improper superimpositions will occur. It is difficult to light a large area like a television studio set evenly with a multiple number of single source incandescent lighting fixtures.
Some effort and innovation has been spent in an attempt to diffuse or spread the light from single source fixtures. This has created some nice lighting effects, but, generally has not solved the disadvantages of high energy consumption, heat generation and uneven lighting.
To improve the lighting in television and video studios certain changes must be made in the way light is generated for production or broadcast. An ideal source of light for television studios and video tape production would be diffuse (not originated from a single point but emitted evenly from a large surface area), generate little heat, be steadfast in its color temperature and offer efficient energy consumption requirements.
I have discovered that a fluorescent tube can be an excellent light source for video and television production. Fluorescent lighting is created within a vacuum tube lined with a blend of oxygen type phosphor materials. An electrical charge is induced at the opposing ends of the tube and generates an ionic discharge that runs throughout the length of the tube. This energizes the phosphor lining, exciting it so that energy in the form of light is emitted. The emission persists for a short time.
Fluorescent lighting has become the most progressive form of lighting today. In pursuit of efficient lighting a great deal of study, development, and refinement of the fluorescent systems has been done.
Traditional fluorescent lighting operates at a rate of sixty cycles per second (some countries operate on a 50 cycles per second rate). This rate is the number of times the phosphor material is excited to its highest level of Light emission within the span of a second. Thus, if you divided a second into sixty parts you would see an arc of discharge for each portion of that second. If one were to slow the process (time-base of the process) spaces could be seen between the light emissions. The glow peaks abruptly on the entire surface of the tube then the glow fades in intensity. So, in a short period of time (one sixtieth of a second) the fluorescent tube has its filaments charged, emits light, then fades. The human eye does not notice these fluctuations at sixty cycles per second.
Motion picture cameras with shutter speeds of 24 or 25 frames per second will record an inconsistent glowing flicker from these lights as they photograph the various light levels of the tube in operation. It is this uneven flicker that has given fluorescent lighting a bad name in media operations. Most lighting directors have seen the uneven flickering of fluorescent lighting in films and believe that fluorescent light is green in color and inconsistent in operation. In truth it is quite consistent but has yet to be optimized to video or television applications.
It is also well understood that fluorescent tubes produce light largely by conversion of ultraviolet radiations from luminescence gas discharges within the tube into visible light through a process called photoluminescence, i.e. a nonthermal emission of electromagnetic radiation by materials called "phosphors" upon excitation or absorption energy from ultraviolet radiations generated in the mercury vapor arc. The absorption and re-radiation of the light at the longer wavelengths by the phosphors is variously described as fluorescence and phosphorescence. The phosphors are typically high purity crystalline compounds which are deposited onto the interior walls of the tube. [See IES Lighting Handbook 5th Ed. 1972, pp 2-8, 2-9.]
By convention fluorescence is defined as the process of emission of electromagnetic radiation by a substance as a consequence of the adsorption of energy from radiation, provided that the emission continues only so long as the stimulus producing it is maintained, i.e., a luminescence which ceases within about 10 nanoseconds after excitation stops. Phosphorescence is defined as luminescence that is delayed more than 10 nanoseconds after excitation stops. [See Van Nostrand's Scientific Encyclopedia 7th Ed. pp. 1194, 1737 and 2189-90.]
The gas within the tube through which the gas discharge or arc is maintained typically includes mercury (Hg) vapor which provides a copious source of ultraviolet radiation when stimulated by collisions with conduction electrons of the electrical discharge or arc which stream between the respective electrodes at either end of the tube. Electrical ballasts supply both the electrical current (typically in pulses) and the necessary potential difference between the respective electrodes at the ends of the tube for maintaining the discharge or arc through the gaseous medium in the tube.
I have discovered that the perfection of solid state electronic ballasts have changed important characteristics of fluorescent lighting. The development of these solid state ballasts have made fluorsecent light something that can be formulated into a superior light source for television and video applications.